Possibly reusable with minor tweaks...

gistfile1.sql

CREATE OR REPLACE FUNCTION notify_changes_on_create() RETURNS trigger
    LANGUAGE plpgsql
    AS $$BEGIN
  PERFORM pg_notify('changes', '{"kind": "create", "data": ' || NEW.data::text || '}');
  RETURN NULL;
END;$$;

CREATE OR REPLACE FUNCTION notify_changes_on_delete() RETURNS trigger
    LANGUAGE plpgsql
    AS $$BEGIN
  PERFORM pg_notify('changes', '{"kind": "delete", "data": ' || OLD.data::text || '}');
  RETURN NULL;
END;$$;

CREATE OR REPLACE FUNCTION notify_changes_on_update() RETURNS trigger
    LANGUAGE plpgsql
    AS $$BEGIN
  PERFORM pg_notify('changes', '{"kind": "update", "data": [' || OLD.data::text || ', ' || NEW.data::text || ']');
  RETURN NULL;
END;$$;

CREATE TABLE IF NOT EXISTS "user" (
    email text NOT NULL,
    data json NOT NULL,
    PRIMARY KEY (email)
);

DROP TRIGGER IF EXISTS notify_changes_on_create ON "user";
CREATE TRIGGER notify_changes_on_create
  AFTER INSERT
  ON "user"
  FOR EACH ROW
    EXECUTE PROCEDURE notify_changes_on_create();

DROP TRIGGER IF EXISTS notify_changes_on_delete ON "user";
CREATE TRIGGER notify_changes_on_delete
  AFTER DELETE
  ON "user"
  FOR EACH ROW
    EXECUTE PROCEDURE notify_changes_on_delete();

DROP TRIGGER IF EXISTS notify_changes_on_update ON "user";
CREATE TRIGGER notify_changes_on_update
  AFTER UPDATE
  ON "user"
  FOR EACH ROW
    EXECUTE PROCEDURE notify_changes_on_update();